Question: In the scene where Goldie Hawn nearly gets her head run over by the car, how do they get that effect? It just looks far too dangerous to be an actual stunt, but it looks too real to be a bluescreen / split screen effect either.
Gary O'ReillyQuestion: What caused Helen and Madeline to break into pieces as they fell down the steps of the church?
Answer: They were warned earlier in the film that they needed to take care of their bodies. But obviously, they put them through a lot of abuse. They didn't take care of themselves, needing to be patched up frequently and whatnot. As a result, at this point, their bodies are like living mannequins more than human bodies. They simply break apart with force, such as falling down the stairs.
TedStixonAnswer: Their bodies had become physically corrupted and fragile from the extreme anti-aging potion, and any stress caused catastrophic damage.
raywest
Question: When Helen and Madelin are fighting with the shovels, Helen whacks off the end of Madelin's shovel, and then Madelin throws the stick through Helen. How did they achieve this effect?
curiouskidChosen answer: CGI, just like any other difficult effect.
Grumpy ScotQuestion: Why does Goldie Hawn wear odd-colored contact lenses to emphasize the fact that her character is dead, but Meryl Streep does not?
Answer: Her eyes changed when she fell into the hot tub. They were essentially boiled.
Jason HoffmanMy interpretation was that when she was shot, she completely bled out, thus all color of her skin and eyes would fade away.
Question: When Streep and Rossellini talk about the potion, Rossellini says "Or as one of my clients simply said -- 'I vant to be alone, yah.'" and Streep replies "No" She's not!" -- Who are they talking about?
Hamster Chosen answer: It's a reference to Greta Garbo who abandoned Hollywood shortly after WWII.
Grumpy ScotQuestion: In the scene when Madeline falls down the stairs, the stunt double appears to take an impossibly hard fall tumbling down those solid marble steps. It is obvious that CGI was used at the start of the fall, when we see Meryl Streep's face hitting the stairs, but during the tumble there was definitely a stunt double used. Do you know if the stunt double did this fall in one take, as it appears in the film, or if special editing was used to make the fall appear harder and faster than it actually was? I can't believe the stunt double could perform such a hard fall without serious injury, but it looks genuine in the film.
Answer: Special editing was used to make the fall seem faster and longer than what it was. If you watch the fall and look closely you can see that two of the shots used were a repeat. The editors used these two shots twice in the fall in order to make the fall appear longer and faster.
oddy knockyQuestion: When Helen and Madelin have finished fighting and they asked Earnest to fix them, how did he fix the great big hole in Helen's stomach?
curiouskidChosen answer: He most likely filled it with something soft, then covered it. You'll notice the lingerie she is wearing completely covers her midsection.
Jason HoffmanQuestion: How come when Lisa is swimming in the pool none of her eyes wash out or anything like the others?
Answer: I don't think she ever died after taking the tonic, unlike Madeline and Helen. She took the potion simply to keep her young good looks and (as stated earlier with Madeline), Lisa is in fact 71 years old with the looks of a 38 year old.
Hamster 
Chosen answer: It is a composite shot, with the actor's head added to the scene. They just did a particularly good job on the scene.
Jason Hoffman